Polypropylene for film capacitor, polypropylene sheet for film capacitor, method for producing the same, and uses of the same

Abstract

A polypropylene for a film capacitor or a polypropylene sheet for a film capacitor which exhibits excellent stretchability when stretched into a film and provides a film having high breakdown voltage and small thermal shrinkage ratio, and which is suitable for a polypropylene film for a film capacitor and a film capacitor comprising the film. The polypropylene for a film capacitor of the present invention is obtained by irradiating a propylene homopolymer with a radiation with an absorbed dose of 0.1 to 500 kGy, the propylene homopolymer having (1) a melt flow rate (MFR) within a range of 1 to 10 g/10 min as determined at 230° C. under a load of 2.16 kg in accordance with ASTM D1238, (2) an isotactic pentad fraction (mmmm fraction) of not less than 94% as determined using 13 C-NMR, (3) an ash amount of not more than 30 ppm as obtained by completely burning the propylene homopolymer in air, and (4) a chlorine amount of not more than 10 ppm as determined by ion chromatography.

The invention claimed is: 
     
       1. A polypropylene for a film capacitor which is obtained by irradiating a propylene homopolymer with a radiation with an dose of 0.1 to 500 kGy. wherein the propylene homopolymer has:
 (1) a melt flow rate (MFR) within a range of 1 to 10 g/10 min as determined at 230° C. under a load of 2.16 kg in accordance with ASTM D1238, 
 (2) an isotactic pentad traction (mmmm fraction) of not less than 98% as determined using  13 C-NMR, 
 (3) an ash amount of not more than 20 ppm as obtained by completely burning the propylene homopolymer in air, 
 (4) a chlorine amount of not more than 10 ppm as determined by ion chromatography, and 
 (5) a melting point (Tm) of not lower than 166° C. as measured by differential scanning calorimetry (DSC). 
 
     
     
       2. The polypropylene for a film capacitor according to  claim 1 , wherein the radiation is an electron beam or a gamma ray. 
     
     
       3. A polypropylene sheet for a film capacitor which is obtained by irradiating a sheet obtained from a propylene homopolymer with a radiation with an dose of 0.1 to 500 kGy, wherein the propylene homopolymer has:
 (1) a melt flow rate (MFR) within a range of 1 to 10 g/10 min as determined at 230° C. under a load of 2.16 kg in accordance with ASTM D1238, 
 (2) an isotactic pentad fraction (mmmm fraction) of not less than 98% as determined using —C-NMR, 
 (3) an ash amount of not more than 20 ppm as obtained by completely burning the propylene homopolymer in air, 
 (4) a chlorine amount of not more than 10 ppm as determined by ion chromatography, and 
 (5) a melting point (Tm) of not lower than 166° C. as measured by differential scanning calorimetry (DSC). 
 
     
     
       4. The polypropylene sheet for a film capacitor according to  claim 3 , wherein the radiation is an electron beam or a gamma ray. 
     
     
       5. The polypropylene for a film capacitor according to  claim 1 . which is obtained by adding a cross-linking agent to the propylene homopolymer. 
     
     
       6. The polypropylene sheet for a film capacitor according to  claim 3 , which is obtained by adding a cross-linking agent to the propylene homopolymer. 
     
     
       7. The polypropylene for a film capacitor according to  claim 5 , which is obtained by adding 0.01 to 10% by weight of a cross-linking agent to 100% by weight of the propylene homopolymer. 
     
     
       8. The polypropylene sheet for a film capacitor according to  claim 6 , which is obtained by adding 0.01 to 10% by weight of a cross-linking agent to 100% by weight of the propylene homopolymer. 
     
     
       9. The polypropylene for a film capacitor according to  claim 1 , wherein the dose of the irradiation is 1 to 300 KGy. 
     
     
       10. The polypropylene sheet for a film capacitor according to  claim 3 , wherein the dose of the irradiation is 1 to 300 KGy. 
     
     
       11. The polypropylene for a film capacitor according to  claim 1 , wherein the propylene homopolymer is in any form of powders, granules and pellets. 
     
     
       12. A polypropylene sheet for a film capacitor which is obtained from the polypropylene for a film capacitor according to  claim 1 . 
     
     
       13. A polypropylene film for a film capacitor which is obtained by biaxially stretching the polypropylene sheet according to  claim 3 . 
     
     
       14. A film capacitor comprising the polypropylene film for a film capacitor according to  claim 13 . 
     
     
       15. A method for producing a polypropylene for a film capacitor which comprises irradiating a propylene homopolymer with a radiation with an dose of 0.1 to 500 kGy, wherein the propylene homopolymer has:
 (1) a melt flow rate (MFR) within a range of 1 to 10 g/10 min as determined at 230° C. under a load of 2.16 kg in accordance with ASTM D1238, 
 (2) an isotactic pentad fraction (mmmm fraction) of not less than 98% as determined using  13 C-NMR, 
 (3) an ash amount of not more than 20 ppm as obtained by completely burning the propylene homopolymer in air, 
 (4) a chlorine amount of not more than 10 ppm as determined by ion chromatography, and 
 (5) a melting point (Tm) of not lower than 166° C. as measured by differential scanning calorimetry (DSC). 
 
     
     
       16. A method for producing a polypropylene sheet for a film capacitor which comprises irradiating a sheet obtained from a propylene homopolymer with a radiation with an dose of 0.1 to 500 kGy, wherein the propylene homopolymer has:
 (1) a melt flow rate (MFR) within a range of 1 to 10 g/10 min as determined at 230° C. under a load of 2.16 kg in accordance with ASTM D1238, 
 (2) an isotactic pentad fraction (mmmm fraction) of not less than 98% as determined using  13  C-NMR, 
 (3) an ash amount of not more than 20 ppm as obtained by completely burning the propylene homopolymer in air, 
 (4) a chlorine amount of not more than 10 ppm as determined by ion chromatography, and 
 (5) a melting point (Tm) of not lower than 166° C. as measured by differential scanning calorimetry (DSC). 
 
     
     
       17. The method for producing a polypropylene for a film capacitor according to  claim 15 , which comprises adding a cross-linking agent to the propylene homopolymer. 
     
     
       18. The method for producing a polypropylene sheet for a film capacitor according to  claim 16 , which comprises adding a cross-linking agent to the propylene homopolymer. 
     
     
       19. A method for producing a polypropylene film for a film capacitor which comprises:
 a step (I) for producing a propylene homopolymer having: 
 (1) a melt flow rate (MFR) within a range of 1 I to 10 g/10 min as determined at 230° C. under a load of 2.16 kg in accordance with ASTM D1238, 
 (2) an isotactic pentad fraction (mmmm fraction) of not less than 98% as determined using  13 C-NMR,    
 (3) an ash amount of not more than 20 ppm as obtained by completely burning the propylene homopolymer in air, 
 (4) a chlorine amount of not more than 10 ppm as determined by ion chromatography, and 
 (5) a melting point (Tm) of not lower than 166° C. as measured by differential scanning calorimetry (DSC); 
 a step (II) for producing a sheet from the propylene homopolymer; and 
 a step (III) for producing a stretched film from the sheet, wherein the method comprises the step for irradiating the propylene homopolymer obtained in the step (I) or the sheet obtained in the step (II) with an electron ray with an dose of 0.1 to 500 kGy. 
 
     
     
       20. The method for producing a polypropylene film for a film capacitor according to  claim 19 , which comprises adding a cross-linking agent to the propylene homopolymer.